Diesel engines are commonly used to propel large motor vehicles such as commercial trucks. An exhaust system of such a diesel engine that comprises a diesel particulate filter (DPF) is capable of physically trapping diesel particulate matter (DPM) in exhaust gas passing through the engine exhaust system. This prevents significant amounts of DPM from entering the atmosphere. Soot is one constituent of DPM. Other constituents include the soluble organic fraction (SOF) and ash (i.e. lube oil additives etc.). The trapping of soot by a DPF prevents what is sometimes seen as black smoke billowing from a vehicle's exhaust pipe.
Unless soot that has been trapped in a DPF is burned off by natural regeneration in sufficient quantity as an engine operates, the continued accumulation of trapped soot will eventually impede exhaust flow. In order to avoid this, regeneration of a DPF may be forced when the quantity of trapped soot has accumulated to some threshold level. One possible strategy for forcing regeneration of a DPF involves using the engine control system to adjust engine fueling in a way that elevates the exhaust temperature to a sufficiently high temperature to combust trapped soot. However, the use of added fuel to force regeneration diminishes the fuel economy of the vehicle that it propels.
The quantity of trapped soot can be monitored in order to ascertain if regeneration should be forced. However, because it is impractical to physically measure the mass of soot trapped in a DPF, the quantity is estimated. The mass of trapped soot can be estimated using an algorithm that processes data representing exhaust flow rate through the DPF and data representing differential pressure across the DPF.